Metal plates provided with irregularity formed by etching the surface thereof are used in various applications, such as elevator doors where a high appearance is required. Etching of a metal plate is performed by corroding the metal using a liquid having a corrosive effect on metal (hereinafter, also referred to as a “etchant”), such as Iron(III) chloride aqueous solution, thereby forming recesses in the metal plate surface. Protrusions, during the etching, are formed by forming a film resistant to the etchant (hereinafter, also referred to as a “resist film”) on the metal plate surface, thereby protecting the region where the film is formed from the etchant to remain as it is without being corroded. Such etching forms irregularity on the metal plate surface. Specifically, the metal plate surface is etched in the steps of: (1) forming a resist film in a region where a protrusion is to be formed on the metal plate surface, (2) corroding by using an etchant a region where the resist film is not formed, and (3) removing the resist film from the metal plate having the region where the resist film is not formed being corroded.
A resist film is conventionally formed in the steps of: (1-1) applying a photosensitive resin onto the metal plate surface, (1-2) adhering a negative film, which transmits light only to a region where a protrusion is to be formed, on the metal plate having the applied photosensitive resin thereon, (1-3) irradiating the metal plate with light through the negative film to cure only an exposed portion of the photosensitive resin, and (1-4) removing a non-exposed, thus non-cured portion of the photosensitive resin. In recent years, resist films are formed by an ink-jet method in some cases. The ink-jet method forms a resist film in the steps of: (1-1′) discharging a composition containing the photosensitive resin from an ink-jet head to deposit the photosensitive resin in a region where a protrusion is to be formed on the metal plate surface, and (1-2′) curing the deposited photosensitive resin by irradiation with an active energy ray.
In these steps, the resist film containing the cured photosensitive resin (hereinafter, also referred to as a “cured resin”) is required to have satisfactory adhesiveness to the metal plate surface. Low adhesiveness to the metal plate surface may cause the resist film to partially separate from the metal plate surface. When the etchant intrudes into the interface between the partially separated resist film and the metal plate surface, metal in the region where the resist film is formed is also disadvantageously corroded.
A resist film formed by curing a curable composition which contains a compound having a phosphoester group in its molecule is known to have high adhesiveness to a metal plate (for example, Patent Literature (hereinafter, referred to as PTL) 1 to PTL 3).
Further, the resist film containing a cured resin is also required to have satisfactory resistance to the etchant (hereinafter, also referred to as “etchant resistance”) and satisfactory solubility in a resist removing liquid which contains a caustic alkali component (hereinafter, also referred to as “alkali solubility”).
In view of those requirements, a resist film formed by curing a curable composition which contains a compound having a carboxylic group and a (meth)acryloyl group in its molecule is known to have high etchant resistance and alkali solubility (for example, PTL 4 to PTL 6).
After the corrosion of the metal plate by using an etchant, the resist film is removed from the metal plate. A resist film is conventionally removed by dissolving the cured resin constituting the resist film in a resist removing liquid containing a caustic alkali component (for example, PTL 7). Such a resist removing liquid is repeatedly used for removing of resist films from metal plates by liquid circulation.